This invention relates generally to apparatus associated with a station for developing electrostatic charge patterns on discrete dielectric sheets with developer material and, more particularly, to apparatus for selectively sealing developer material within a developer station and, during sealing, guiding moving discrete dielectric sheet out of developing relation with such developer material.
In U.S. Pat. No. 4,436,405 issued Mar. 13, 1984 in the name of Kindt, an electrographic copier is described which utilizes a plurality of discrete dielectric sheets respectively including a photoconductive layer. The discrete sheets are transported seriatim about a continuous path into operative relation with electrographic process stations to make information reproductions. In the reproduction process carried out at such process stations of the copier, a discrete dielectric sheet is uniformly charged and then exposed to an image of information to be reproduced (e.g., a document) to form an electrostatic charge pattern on such sheet corresponding image-wise to such information. The charge pattern is developed with pigmented thermoplastic electroscopic marking particles electrostatically attracted to the charge pattern to form a transferable image. The transferable image is then transferred from the sheet to a receiver member to form the information reproduction, and the sheet is cleaned for reuse.
The development of the charge patterns on the discrete dielectric sheets is accomplished by a magnetic brush developer station. In a typical magnetic brush developer station, developer material including pigmented electroscopic marking particles adhering to magnetizable particles (or single component material where the pigmented particles are in themselves magnetizable) are brought into a magnetic field intercepting the path of a moving electrostatic charge pattern carrying member. The magnetizable particles align in the magnetic field to form a brush-like bristle nap of pigmented particles which contact such member. The pigmented particles are electrostatically attracted from the nap to the charge pattern and adhere to such pattern for development. However, when the charge pattern carrying member is a discrete sheet, there is a propensity for the leading edge of such sheet to plow through the bristle nap. This can lead to deposition of developer material on the back side of the sheet. Therefore, cleaning of the sheet is made more complex (i.e., the back side as well as the front side must also be cleaned). Moreover, contamination within the copier environment by airborne developer material, or non-transferred developer material carried out of the magnetic brush developer station by the sheet, is potentially increased.
In the commonly assigned copending U.S. patent application Ser. No. 633,564, filed July 23, 1984, in the name of Crandall, a mechanism is disclosed which prevents a moving discrete dielectric sheet from plowing through a bristle nap of a magnetic brush developer station. Such mechanism includes a movable belt in contact with the developer station and overlying the bristle nap to seal developer material of such nap within the developer station. The belt has an opening substantially congruent with the image (charge pattern bearing) area of a discrete dielectric sheet. The belt and sheet are moved in timed relation so that the image area of the sheet overlies the belt opening as a sheet is moved into developing relation with the nap. Thus, the marginal edges of the sheet are shielded by the belt and the image area is located so as to be developed by material from the nap. While this mechanism is successful in preventing the sheet from plowing through the magnet brush bristle nap, it requires accurate interrelated control of movement of the shielding belt with the sheet to ensure the alignment of the belt opening and the sheet image area during development.